1. Field of the Invention
This invention relates to blends of aromatic carbonate polymers with acrylonitrile-styrene-butadiene (ABS) resins, further blended with certain acrylate copolymers for gloss reduction.
2. Brief Description of the Prior Art
Molded products made of thermoplastic resins are frequently glossy. For some purposes, this is desirable, however, a matte or non-glossy surface is often preferable for products such as housings for computer terminals, typewriters, miscellaneous electrical appliances and certain automotive parts.
Elimination of gloss by surface embossing requires a separate step and adds cost, moreover, subsequent abrasion may remove the embossed matte surface and cause the gloss to reappear. The addition of a delustering agent such as finely-divided silica, silicate, alumina, or other mineral filler often has a detrimental effect on physical properties such as impact strength. Attempts to add a polymeric delustering agent frequently also have deleterious effects on physical properties, not only on impact strength but also on heat distortion temperature, weathering, light stability, and other important properties.
The reduction of gloss is known to occur by adding substantial amounts of certain other polymers to make thermoplastic blends, for instance by the addition of special copolymers crosslinked by means of allyl functionality, as described in U.S. Pat. 4,460,742. However, the incorporation of substantial amounts of incompletely compatible resins frequently has an adverse effect on strength properties, causing delamination and weak weld lines in molded parts, and on cost.
Blends of aromatic carbonate polymers with acrylonitrile-butadiene-styrene (ABS) resins are very useful plastics in view of good processing characteristics and physical properties, but they tend to be glossier than desired, especially at the low percentages of ABS used to achieve high heat distortion temperatures. Efficient means are needed for making low gloss polycarbonate-ABS blends, while allowing the formulator latitude to use many different grades of ABS and especially to use low levels of ABS where high heat distortion temperature is required. To achieve low gloss without compromising other desirable properties of the polymer necessitates that the low gloss producing means must require only small amounts, i.e. 10% or less, of polymeric additives. Thus, any additive employed to achieve low gloss must permit retention of the excellent processing characteristics and physical properties of polycarbonate-ABS blends, while avoiding delamination and assuring strong weld lines in the molded parts. It has hitherto been especially difficult in polycarbonate-ABS blends to satisfy simultaneously requirements for low gloss and high heat distortion temperature.
Our copending application, filed on even date with the present application, teaches the blending of aromatic carbonate polymers with certain specific acrylonitrile-butadiene-styrene (ABS) copolymers which obviate the need for a specific additional ingredient in order to achieve low gloss with good physical properties. The present application presents an alternative approach to the same objective, and which has the feature of allowing a wide latitude in choice of ABS type and level. This latitude is achieved by the use of a specific third inqredient to obtain the low gloss characteristics desired for the blend.